[Bug ld/28686] [avr] linker relaxations generate incorrect value

[nickc at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28686

Nick Clifton <nickc at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-12-16
           Assignee|unassigned at sourceware dot org   |nickc at redhat dot com
                 CC|                            |nickc at redhat dot com
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1

--- Comment #1 from Nick Clifton <nickc at redhat dot com> ---
Hi Joerg,

  The root cause for this problem is the assembler.  When it assembles
  the test file it created a relocation for the LDI instruction which 
  references the .text section:

    % objdump -dr main.o
    [...]
     4b2:       f0 e0           ldi     r31, 0x00       ; 0
                        4b2: R_AVR_HI8_LDI      .text+0x500

  So when the relaxation happens the code adjusts the relocation
  eventually ending up with .text+0x2ab which then translates into
  a value of 2 (the top 8 bits of the addition) for LDI instruction.

  This error of course is that the relocation should not be against
  an offset from the .text section, but rather against the matrix
  symbol itself.  Since this symbol stays aligned, it does not move
  as far back as the .text+offset value.

  I am currently testing a local patch which stops the assembler
  from trying to optimize away symbol names in relocations if it
  knows that linker relaxation is going to occur.  With this patch
  applied the object file looks like:

   % objdump -dr main.o
   [...]
    4b2:        f0 e0           ldi     r31, 0x00       ; 0
                        4b2: R_AVR_HI8_LDI      matrix

  And when finally linked the correct value - 3 - is used by the 
  LDI instruction.

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